Starship Trader Monthly is a catalog of generated science fiction space vehicles. Presented in a "classified ads" format, each item in the catalog comes with a brief description, and a 3d rendered picture of the subject.
The actual text of the book is significantly less than 50,000 words. But since the book is mainly a frame to show pretty pictures, and the common exchange rate is "One Picture == One Thousand Words", there is another way to meet the NaNo requirement: the book contains 50 pages of generated pictures (48 pages, plus front and back cover), thus the equivalent of 50,000 words.
The code used to produce the catalog is called "Star And Driver", a pun on the popular auto magazine that I am too stubborn to change now. It is written in Perl, as a main script and several modules. The images are rendered by passing a procedurally generated script to POV-Ray. Text generation is through custom Perl text smashing, with data sources taken from dariusk/corpora. PDF::API2 is used to collect all text and images together, laying them out into the final format.